This section provides background information to facilitate a better understanding of the various aspects of the invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
A vertical ground heat exchanger comprises at least one vertically-drilled hole (borehole) in a geological formation. Depending upon the application and contractor preferences, boreholes can vary in diameter and depth to a significant degree.
The borehole contains one or more vertical closed loops (VCLs), each comprising two pipes joined at the bottom of the hole with a u-shaped bend or fitting. The vertical closed loops (VCLs) are connected at the top of the hole to the supply and return sections of a fluid transfer system. The vertical closed loops (VCLs) and fluid transfer system are used to transport a heat transfer fluid that will carry heat to or from the geological formation.
Installation of vertical closed loops (VCLs) is followed by filling of the voids in the drilled borehole with a grouting material to provide a suitable medium for transfer of heat between the VCLs and the ground and to seal the borehole. Properly sealing the borehole by grouting the void space between the vertical closed loops piping and the borehole will protect aquifers from contamination and loss of natural artesian pressure. Grouting material is conveyed to the entire depth of the drilled borehole through use of a tremie line that is typically pulled up during the grouting process to reduce pumping pressure.
An important factor in the efficiency of a vertical ground heat exchanger is the proximity between the vertical closed loop pipes used to transfer heat to and from the geological formation and the wall of the borehole in the formation. Basic and conventional systems, shown in FIG. 1, make no particular effort to improve this proximity.
Referring to FIG. 2, a known method of improving proximity between the pipes and the geological formation is to use mechanical clip spacers. U-tubes with mechanical clip spacers in vertical ground heat exchangers improve the proximity and the benefits of improving this proximity are well documented: adding 20-35% higher efficiency by reducing thermal resistance in the borehole. The current practice of using plastic/metal clips at spaced intervals in the ground lacks uniformity in the amount of spreading.